Phosphorus Stress Effects on Growth and Seed Yield Responses of Nonnodulated Soybean to Elevated Carbon Dioxide

The influence of P availability on plant responses to elevated atmospheric CO 2 concentrations has received limited research attention. Therefore, an experiment was conducted to examine the effect of a wide range of P availabilities on plant response to enriched atmospheric CO 2 . Nonnodulating soybean [ Glycine max (L.) Merr., ‘Lee’] plants were grown from germination to maturity in controlled environment chambers at 350 or 700 μL L −1 CO 2 and supplied with a complete nutrient solution containing either 0.005, 0.10, 0.25, 0.50, or 1.00 m M P. Growth and seed yield were maximized at the 0.25 and 0.50 m M P concentrations at 350 and 700 μL L −1 CO 2 , respectively. Growth and yield were significantly increased by CO 2 enrichment at all except the lowest P concentration. The stimulation of growth at high CO 2 was consistently associated with increased leaf area, net assimilation rate, P uptake, and P utilization efficiency in the production of dry matter. When averaged over the four highest P levels, total root mass was increased 63% by CO 2 enrichment, but P uptake efficiency per unit root mass was decreased 22%. The yield enhancement of 23 to 57% at high CO 2 was associated with increases in the number and size of seed. Carbon dioxide enrichment had no significant effect on harvest index. The results indicate that CO 2 enrichment can result in stimulation of growth and yield of nonnodulated, NO − 3 ‐fed soybean plants, even at concentrations of P that limit plant growth at ambient CO 2 concentrations.